AUSTRALIAN SOUTHERLY BUSTERS .3. THE PHYSICAL-MECHANISM AND SYNOPTIC CONDITIONS CONTRIBUTING TO DEVELOPMENT

The physical mechanism responsible for the formation of the southerly buster is investigated using simulations from a version of the Austral ian Bureau of Meteorology's numerical weather prediction model. Froude number calculations are performed on a numerically simulated event to determine the blocking capacity of the mountains while the separate r oles of the southern and eastern topography are explored through a ser ies of idealized topography simulations. It is found that the topograp hy along the southern coastline plays a crucial role in the formation of the southerly buster through blocking of the cold air and subsequen t channeling around to the east coast where the southerly surge occurs . The interaction of four other summertime cold fronts with the southe astern Australian topography is studied. Only two of these events in r eality produced southerly busters on the east coast. The model demonst rates ability to simulate the additional fronts accurately and hence d istinguish between the southerly buster events and nonevents. The addi tional simulations are found to substantiate the results of the first part of the study in terms of demonstrating the importance of the orie ntation of the synoptic-scale front with respect to the southern coast line.